Methods and apparatus for providing emergency telephone service to IP-based telephone users

ABSTRACT

For purposes of servicing emergency calls, such as 911 calls, a telephone number is associated with each edge router port used to provide IP service to a customer premise location. A telephone number is associated with the edge router port and the corresponding customer location. The telephone number and location information are stored in a database used for providing emergency calling party location information. When a switch used for routing IP calls detects a telephone call to an emergency call center it determines the edge router port from which the call was placed and the telephone number associated with the port for emergency call purposes. The call is then forwarded to the emergency call service center with the determined telephone number being supplied as the calling party number. Performing a lookup operation using the supplied telephone number the emergency service operator determines the location from which the call was placed.

RELATED APPLICATIONS

The present invention is a continuation of allowed U.S. patentapplication Ser. No. 10/457,111 filed Jun. 9, 2003 which claims thebenefit of U.S. Provisional Patent Application Ser. No. 60/455,353,filed Mar. 17, 2003 titled “Methods and Apparatus For Supporting IPTelephony” and is a continuation-in-part of U.S. Utility patentapplication Ser. No. 10/337,106, filed on Jan. 6, 2003 titled “MethodsAnd Apparatus For Determining The Port And/Or Physical Location Of An IPDevice And For Using That Information” which claims the benefit of U.S.Provisional Patent Application Ser. No. 60/346,596, filed Jan. 8, 2002titled “Methods And Apparatus For Determining The Port And/Or PhysicalLocation Of An IP Device And For Using That Information”, each of whichis hereby expressly incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention is directed to communications systems and, moreparticularly, to methods and apparatus for integrating IP-basedtelephone users into known emergency telephone services, e.g., 911.

BACKGROUND OF THE INVENTION

Digital communications networks have continued to grow in importance aspeople have come to rely on the electronic exchange of information tosupport both business and personal pursuits. E-mail, the electronictransfer of files, and various other services are made possible by theuse of digital communications networks.

The type of digital communications network employed often depends on thesize of the network to be implemented, as well as the needs andcapabilities of the party or parties implementing the network. Hardwarecost and network management complexity are often a factor when choosingthe type of network to be implemented.

Networks limited to a small geographical region, e.g., home or singleoffice location, are frequently called local area networks (“LANs”).LANs are often privately-owned networks within a single building orsmall campus. LANS are widely used to connect personal computers andworkstations at a single location, e.g., company office or residence, toone another and to shared resources such as printers and/or localcentralized file storage.

One popular type of LAN, an IEEE 802.3 standard based LAN is popularlycalled Ethernet. Ethernet is a bus based broadcast network withdecentralized control. When using Ethernet, data, e.g., messages,information and signals are transmitted in Ethernet using frames.Ethernet devices broadcast and receive frames over the shared bus overwhich the frames are broadcast. The format of an IEEE 802.3 frame 100 isshown in FIG. 1. Each frame 100 starts with a 7 byte preamble 102containing a preset bit pattern. The preamble 102 is followed by a startof frame byte 104 which includes the bit pattern 10101011 used to denotethe start of the frame. Next come two addresses, a destination address106 and a source address 108. The high-order bit of the destinationaddress is a 0 for ordinary addresses and 1 for group addresses. Groupaddresses, in contrast to individual device addresses, allow multiplestations, e.g., devices coupled to the Ethernet, to receive framesincluding a single group address. When a frame is sent to a groupaddress, all the stations in the group receive it. Sending to a group ofstations is called a multicast. The address consisting of all 1 bits isreserved for broadcast. A frame containing all is in the destinationfield, indicating a broadcast, is delivered to all stations on thenetwork.

Six byte global Media Access Control (MAC) Ethernet device addresses areassigned by a central authority to ensure that no two stations on thesame Layer 2 network, e.g., Ethernet LAN, have the same global address.Manufacturers of Ethernet devices, e.g., networking boards, request ablock of addresses from the central authority to assure that no twoEthernet boards are assigned the same global MAC address. The boardsthen send and receive frames based on the 48-bit MAC address programmedinto the board by the manufacturer. Because source MAC addressinformation is inserted into Ethernet frames by the Ethernet boards, thesource address 108 in an Ethernet frame is usually accurate and isdifficult to fake.

Since Ethernet MAC address are unique at least on the same Layer 2network, and potentially globally, any device on a Layer 2 network canaddress any other device on the network by just using the right 48 bitMAC address assigned to the device being addressed.

MAC addresses are data link layer addresses. The data link layercorresponds to the second layer of the seven layer OSI (Open SystemsInterconnection) Reference Model. As a result, Ethernet LANs and otherLANS which use data link layer addresses are sometimes called Layer 2networks.

In addition to the address information 106, 108 the Ethernet frameincludes a length of data field 110, data field 112, padding field 114and a checksum field 116. As will be discussed below, informationintended to be transmitted over an IP based network may be included inthe data field 112.

While Layer 2 networks are well suited for implementing LANs, e.g., atrelatively small sites, it is often desirable to connect devices, e.g.,computers located on different LANs. Layer 3 networks, which rely onnetwork protocols, e.g. TCP/IP protocols, are often used forinterconnecting Layer 2 networks. Layer 3 packets, e.g., IP packets, areoften encapsulated in Layer 2 frames to extend the reach of the Layer 3network to host devices on the Layer 2 network. This permits Layer 2signaling and frames to be used for transmissions of data over theEthernet while preserving Layer 3 addressing information fortransmission over the Layer 3 network. The network resulting frominterconnecting one or more Layer 2 and Layer 3 networks is oftenreferred to as an internet.

The Internet is a well-known worldwide internet that is used to connectcomputers and other devices located at universities, governmentsoffices, businesses and individuals together.

FIG. 2 is an extremely simplistic representation of the Internet 200. Asillustrated, the Internet 200 includes a plurality, e.g., first andsecond, Layer 2 networks 201, 203, coupled together by a Layer 3 network205. While only two Layer 2 networks, e.g., Ethernet LANs, are shown,many thousands of such networks may be part of the Internet. Edgerouters, e.g., multi-protocol routers, capable of converting betweenLayer 2 and Layer 3 formats and addressing schemes, are often used toconnect Layer 2 networks to Layer 3 networks. In FIG. 2, first edgerouter 216, connects the first Layer 2 network 201 to the Layer 3network 205. Similarly the second edge router 218 connects the secondLayer 2 network 203 to the Layer 3 network 205.

In the FIG. 2 example, two host devices 208, 210 are shown coupled tothe first Ethernet bus 204, used to implement the Ethernet LAN 201,while third and fourth host devices 212, 214 are shown coupled to thesecond Ethernet bus 206 used to implement Ethernet LAN 203. While onlytwo hosts are shown on each Ethernet LAN it is to be understood that alarge number of hosts may be coupled to any one of the Layer 2 networks,corresponding to Ethernet busses 204, 206, at any given time.

Routers, serve as forwarding devices and, optionally, protocolconversion devices. In the FIG. 2 diagram, edge routers 216 and 218 havethe capability of converting between Ethernet frames and IP packets, andvice versa, using one or more tables relating IP addresses to MACaddresses.

Routers 222, 224, 226 and 228 internal to the Layer 3 network form partof what is sometimes called the Internet backbone. Since these routersdo not need to handle Ethernet frames, they do not include the protocolconversion functionality present in the edge routers 216, 218. Groups ofrouters 216, 218, 222, 224, 226, 228 managed by a single administratoris often called an Autonomous System (AS). The Internet includes severalAS which are connected to each other. Each AS may include one or moreDHCP (Dynamic Host Configuration Protocol) servers which are responsiblefor assigning IP addresses to host devices connected to the AS. In FIG.2, a single DHCP server 220 is shown coupled to edge routers 216, 218

Unlike LANs which use data link layer addresses, the Internet uses Layer3 (Network layer) addresses, e.g., IP Addresses, for purposes ofidentifying source and destination devices and determining theappropriate route upon which packets should be transmitted. Source anddestination IP addresses are included, along with data, in IP packetsused to transmit information across the Internet. Every host and routeron the Internet has an IP address which encodes its IP network numberand host number. The combination is unique, no two machines have thesame IP address.

Exemplary IP addresses are 32 bits long and are used in the Sourceaddress and Destination address fields of IP packets. FIG. 3 is adiagram 300 which illustrates the standard 32 bit format for IPaddresses. Note that host addresses are divided into different classes(A, B, C) with different numbers of bits allocated to the network numberand host portion number in each address class. From a managementperspective, system administrators may divide the host number portion ofa 32 bit IP address into a subnet portion 402 and a host portion 404 asillustrated in block 400 of FIG. 4. In such embodiments, within thenetwork defined by the network portion of the IP address, a subnet maskis used at the routers within the network to distinguish between thehost portion 404 and the rest of the 32 bit IP address and thereby allowfor routing within the network based on the subnet portion of theaddress.

The demand for IP address continues to grow and, with fewer bits thanare used for MAC addresses, there are considerably fewer IP addressesavailable for allocation. Given the demand for IP addresses and thelimited supply, IP addresses are leased from a central authorityresponsible for overseeing their allocation. Internet service providers,may lease a large number, e.g., a block of IP addresses, which theprovider then sub-leases to end users, e.g., host devices.

As a result of the lease (actually the sub-lease) process, end usersobtain an IP address which is subject to lease restrictions includingthe right to use the IP address for a limited period of time. IPaddresses leased for extended periods of time, e.g., a year or more, areoften termed “static” IP addresses. Static IP addresses are used forapplications such as Web site hosting where the Internet connection islikely to remain active and in use for extended periods of time. Usersnormally pay a premium for static IP addresses.

With regard to individual Internet users, IP addresses are more commonlyleased to end users on a dynamic basis. Internet service providersfrequently use a DHCP server to assign users IP addresses for a limitedlease time when they seek to access the Internet, e.g., from a hostdevice coupled to the Internet by way of a Layer 2 network. FIG. 2illustrates a single DHCP server 220 coupled to the two edge routes 216,218 to oversee IP address allocation. In practice, the Layer 3 network202 may include multiple DHCP servers with each server being responsiblefor allocating IP addresses to users on a different network or subnet.The system administrator responsible for overseeing an AS determines therelationship between DHCP servers, sets of IP addresses allocated byeach of the DHCP servers and the edge routes which connect users to theDHCP servers for IP address assignment.

Once an IP address is leased to a host, e.g., user, if the host remainsactive beyond the lease term, the lease may be extended or a new IPaddress assigned to the host from the available pool of IP addresses atthe end of the first lease term.

When a user intends to stop using the IP address, the user's device,e.g., host device 208, normally signals to the DHCP server that assignedthe IP address that the address is being released. This allows theaddress to be added to the pool of available addresses and reused. Inthe event that a release message is not received prior to the IP addresslease timing out, and the DHCP server encounters a shortage of addressesin the pool of available addresses, the DHCP server may poll devices towhich it allocated IP addresses to see if they are still active. Failureto receive a response may result in the DHCP adding the IP addressassigned to the non-responding device back into the pool of available IPaddresses.

Thus, unlike MAC address which are fixed for the life of a product bythe manufacturer, the IP address assigned to a particular host devicecan change from moment to moment. Accordingly, in contrast to MACaddresses which are fixed for the life of a product by the manufacturer,there is no permanent fixed relationship between a physical device andthe IP address assigned to the device.

Many contemplated IP applications could benefit from reliableinformation about the location and/or identity of a host device using anIP address. The dynamic allocation of IP addresses and re-use of IPaddresses discussed above, greatly complicates attempts to accuratelycorrelate specific devices and/or physical locations with an IP address.

The problem of associating IP addresses with physical locations isfurther complicated by the manner in which IP addresses are assigned andused. Blocks of IP addresses are assigned by the central authority todifferent network providers based on the size of their networks. Unlikezip codes or telephone number area codes, assignment of IP addresses isindependent of geographic location. Accordingly, IP addresses do notinherently convey geographic location information as do, for example,zip codes used by the post office or the area code portion of atelephone number.

Reliable location information is also difficult to obtain in an IPnetwork because IP based routing relies, in most cases, on theintelligence of the network to determine the routing path to a specifieddestination address. The host need not, and in most cases does not, knowthe physical location of the destination device to which it is sendingpackets or the route over which the transmitted packets will beconveyed. In addition, routers in an IP network usually only need todetermine the next router in a path based on an IP address and thereforeoften do not include detailed topology information relating to largeportions of an IP network. While shielding end devices and routers fromhaving to make end to end routing decisions has many advantages, thelack of information about the physical devices corresponding to IPaddresses poses problems in many contemplated IP based applications.

IP based services, those based on private internets and the largerInternet are continuing to grow in importance. IP and the Internet arebeginning to be used for a wide range of applications such as music filesharing, news delivery, software distribution, etc. IP and Internetapplications which are expected to grow in importance in the futureinclude Internet telephony and video on demand services. In the case ofInternet telephony voice signals are exchanged over the Internet throughthe use of packets including voice data. In the case of video on demand(VoD) services, video in the form of digital files transmitted aspackets, is supplied to a customer using the Internet as the transportmechanism.

In many cases, it would be useful if the physical location of a deviceusing an IP address could be determined from its IP address. Oneparticularly relevant and important application where IP device locationis important is the servicing of IP telephony calls by emergency servicecall centers such as 911 call centers.

Unfortunately, there is currently no simple way to convey physicallocation information to a 911 operator from an IP network. Accordingly,not only does determining the originating location of an IP call presentproblems but conveying such location information to an operator alongwith an IP based 911 call is particularly challenging.

In the case of existing 911 service for landline phones, calling partytelephone number information is forwarded over the PSTN to a 911emergency call center as part of the standard automatic numberidentification information provided as part of standard SS7 signalingassociated with a telephone call. The emergency call center uses thecalling party's telephone number to access a 911 database whichcorrelates telephone numbers to physical locations, e.g., the address ofthe telephone service subscriber to which the telephone number isassigned. Entries in the 911 telephone number/location database areupdated infrequently, e.g., usually with the assignment or reassignmentof a landline telephone number. Usually the information for a specifictelephone number is entered at the time the telephone number is assignedand frequently remains unmodified until telephone service for theparticular number is discontinued. Currently there is no easy way tofrequently update the contents of the existing 911 location informationdatabases to reflect a phone, e.g., an IP phone, being moved fromlocation to location.

In view of the above discussion, there is a need for methods andapparatus for providing calling party location information to anemergency 911 service center when the center is servicing a callassociated with an IP telephony device. It is desirable that suchlocation information can be provided in a way that avoids the need tomake significant or costly modifications to current 911 locationinformation database systems or to add significant amounts of hardwareto such systems. From the emergency service center perspective, it wouldbe ideal if accurate location information could be obtained regardlessof whether a call is placed from an IP telephony device or a landlinephone in the same manner that location information is currentlyretrieved for landline calls.

SUMMARY OF THE INVENTION

The present invention is directed to methods and apparatus for providinglocation information to an emergency call center, e.g., a 911 callcenter, for calls placed from IP telephony devices.

In accordance with the invention IP phones register with an IP switch,e.g., a soft switch, which has access to stored information associatingthe IP phone's telephone number with an IP address. The IP addressassigned to a phone may vary at any specific point in time, e.g.,depending on factors including which router port is used to couple thephone to the IP network. Since IP addresses can be assigned dynamically,each time an IP phone is reconnected to the IP network, the IP telephonydevice updates the IP address information associated with its assignedtelephone. Calls to/from an IP telephone are then directed based on theupdated IP address information maintained by the soft switch.

As a result of the soft switch registration process calls to an IPtelephone number may be routed from/to different locations at differenttimes depending on the physical location of an IP telephony device.Accordingly, an IP phone number, unlike a landline number, normally doesnot have a fixed physical location associated with it and therefore doesnot provide accurate location information since the phone number is nottied to a specific location.

In accordance with the present invention, for purposes of servicingemergency calls, e.g., for E-911 purposes, a telephone number isassociated with each edge router port associated with a specificlocation, e.g., office, residence, etc., that may be used to support anIP telephone. A telephone number associated with the edge router portand the corresponding location information is stored in an emergencylocation information database, e.g., an existing database used forproviding 911 calling party location information for calls from landlinephones. The telephone number may be, e.g., the number of a landlinephone located at a customer premise location to which the edge routerport is connected or a telephone number which is not actually used toprovide telephone services but is used, in accordance with the presentinvention, as a way of conveying location information. Normally thetelephone number associated with the edge router port will be differentthan the telephone number associated with an IP phone for purposes ofrouting calls to the IP phone.

When the soft switch of the present invention used for routing IP callsdetects a telephone call to an emergency call center, e.g., a 911 call,it determines the edge router port from which the call was made.

This can be done using the IP address associated with the callingparty's IP telephone and the techniques discussed below. Once the edgerouter port is identified, the soft switch performs a look-up operationto determine the telephone number associated with the port for emergencycall purposes. This telephone number may correspond to a telephone whichis not registered to the IP caller. In fact, it may even correspond to atelephone number which is not even in active use for placingand/receiving calls. Significantly, however, the telephone numberassociated with the utilized edge router port corresponds to thelocation from which the IP telephony call is placed, e.g., the locationof the customer premise corresponding to the edge router port throughwhich the IP call was received.

The IP based call to the emergency call center, referred to herein forpurposes of explanation as a 911 call, is routed to PSTN by an IP toPSTN gateway with the telephone number retrieved from the look-upoperation being supplied as the calling party number instead of theactual calling party number. Upon receiving the 911 call, the 911service center performs an address look-up operation using the suppliedcalling party number in the normal manner. This results in the addressassociated with the port from which the IP-based call was placed beingsupplied to the 911 operator along with the voice portion of the IPtelephone call. This calling party number can be used to determine thephysical location of the calling party.

Significantly, hardware modifications to existing emergency locationinformation databases which associate telephone numbers with customerpremise locations are not required to implement the present invention.The location information databases merely need to be loaded withtelephone numbers, and corresponding physical customer premise locationinformation, that are associated in accordance with the presentinvention with edge router ports used to provide IP telephony service.Such telephone number and address information may be loaded into the 911database at the time IP service is initially provisioned for a customerpremise and left unchanged until service to the customer premise throughthe port is terminated. Thus, updates to the emergency locationinformation database corresponding to individual customer premisesthrough which IP telephone service may be provided can be relativelyinfrequent, e.g., the same or about as frequent as the data base isupdated in regard to landline phones.

Accordingly, without requiring modifications to the existing PSTNportion of the 911 system, emergency service telephone operators can besupplied with location information for IP based calls. This informationcan then be used, e.g., to dispatch emergency services to the source ofthe call to the 911 telephone call.

Numerous additional embodiments, features and applications for themethods and apparatus of the present invention are discussed in thedetailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an Ethernet frame.

FIG. 2 is a simplified Internet diagram.

FIG. 3 illustrates the 32 bit IP addressing scheme used for Internetaddresses.

FIG. 4 illustrates the components of a 32 bit Internet address havingthe illustrated subnet mask.

FIG. 5 illustrates a communications system implemented in accordancewith the invention.

FIG. 6 illustrates an edge router implemented in accordance with theinvention.

FIGS. 7-9 illustrate various tables included in the edge router of FIG.6.

FIG. 10 illustrates a DHCP server responsible for dynamically assigningIP addresses and for storing information relating to said addresses inaccordance with the present invention.

FIG. 11 illustrates a location and customer information server (LCIS)implemented in accordance with the invention.

FIG. 12 illustrates a router and port number to customer (RPC)information database implemented in accordance with the invention.

FIG. 13 illustrates a routine for providing customer informationcorresponding to an IP address in response to information requests.

FIG. 14 illustrates a soft switch implemented in accordance with thepresent invention.

FIG. 15 illustrates a 911 operator center implemented in accordance withthe present invention.

FIG. 16 illustrates an E911 routine implemented by a soft switch inaccordance with the present invention.

DETAILED DESCRIPTION

FIG. 5 illustrates a communication system 500 implemented in accordancewith the present invention. As will be apparent from a review of FIG. 5,the communication system 500 has many elements which are the same as orsimilar to the elements of the existing Internet as shown in FIG. 2.Elements in FIG. 2 and FIG. 5 which are the same as, or similar to, oneanother are indicated using the same reference numbers in both figures.Such elements will not be described again in detail.

The system illustrated in FIG. 5 includes first and second Layer 2networks 501, 503, e.g., Ethernet LANs, coupled together by a Layer 3,e.g., IP based, network 505. In addition to the IP based network 505,the system 500 includes additional networks 530 and customer premises533 which are in addition to the layer 3 network 505. The additionalnetworks include a service management network (SMN) 532 and a publicswitched telephone network 531. One or more conventional (e.g., non-IP)telephone devices 535 may be coupled to the PSTN 531. In FIG. 5, forpurposes of illustration, a single telephone 535, located at a customerpremise 533, is shown coupled to the PSTN 531. In practice many suchtelephone devices located at different customer premises are normallycoupled to the PSTN 531.

The first Layer 2 network, e.g., LAN 501, includes host devices 208, 210coupled to Ethernet bus 204. The LAN 501 is located at a first customerpremise (CP) 521. Similarly, the second Layer 2 network 503 includinghost devices 212, 214 coupled to Ethernet bus 206. The LAN 503 islocated at a second CP 523. Each CP 521, 523, corresponds to a singlephysical location, e.g., an office building or home, for which locationinformation can be stored in the SMN 532.

An IP based network 505 couples the first and second Layer 2 networks501, 503 together. The IP based network 505 includes first and secondedge routers 516, 518, a DCHP server 520, core routers 222, 224, 226,228 and a soft switch (SS) 536.

The first and second edge routers 516, 518 serve as the interfacebetween the Ethernet LANs 501, 503, respectively, and the IP 505. Whilethe edge routers 516, 518 perform the same functions as edge routers216, 218 as will be discussed further below, they also include routinesfor responding to requests to identify a router port corresponding to anIP or MAC address supplied as part of a port information request.

The DHCP server 520 is responsible for dynamically assigning IPaddresses while the SS 536 is responsible for interfacing between the IPnetwork 505 and public switched telephone network (PSTN) 531. The softswitch stores information associating IP address of telephone deviceswith telephone numbers. It is responsible for routing IP telephone callsbetween IP telephone devices over the IP network 505 and for performingthe necessary protocol conversions required to bridge and routetelephone calls between the IP domain and the PSTN 531. Routing oftelephone calls between the IP and PSTN domains may be required, e.g.,when a telephone call between an IP device and a conventional PSTNtelephone occurs.

To facilitate the secure exchange of customer and management informationbetween system components, e.g., routers and servers in the system 500,the system 500 includes a secure management network (SMN) 532. The SMN532, which may be implemented using IP, is in addition to the Layer 3network 505.

As an alternative to using a separate network for the exchange ofmanagement and customer information, secure communications channels canbe implemented between system components, e.g., routers and servers,using encryption and/or other virtual private networking techniques.Accordingly, customer and management may be transmitted over separatephysical communications channels or secure communications channelsprovided using existing communications links between network elements.

Various elements are incorporated into the SMN 532 including a locationand customer information server (LCIS) 534 implemented in accordancewith the invention. As will be discussed below, in accordance with thepresent invention, the LCIS 534 includes a router-port to customerinformation (RPC) database 537. The RPLC database 537 includes sets ofcustomer records created, e.g., when a customer subscribers to an IPservice provider. As will be discussed below each record may include,e.g., customer premise location information, name, address and landlinetelephone number information. Each customer record is correlated to anedge router and port which is assigned to be used by the customer whenaccessing the IP network via a LAN or other connection.

For various applications, e.g., servicing of 911 emergency telephonecalls, the SS 536 and/or other network devices coupled to the SMN 532may request the location and/or other customer information associatedwith a particular IP address of interest, e.g., the IP address used toinitiate a 911 calls from an IP telephone. As will be discussed below,the LCIS 534 includes routines for responding to such informationrequests.

An emergency call center, e.g., a 911 operator center 560, is coupled tothe PSTN 531. While a single 911 operator center 560 is shown, it is tobe understood that there may be several 911 operator centers locatedacross the country which service different geographic areas. These 911operator centers 560 provide emergency telephone services, e.g.,dispatching firemen and/or ambulances. The 911 operator center 560includes a location information database shown in FIG. 5 as a 911database 561. The location information database 561 includes phonenumbers and corresponding customer premise addresses. A 911 telephoneoperator handling an emergency call can access the database 561 using acalling party's telephone number obtained from ANI informationassociated with the voice portion of an incoming call in accordance withstandard SS7 signaling, and retrieve from the database the location ofthe caller. This is particularly useful in cases where the 911 caller inunable to tell the operator their current location, e.g., as a result ofbecoming incapacitated or because of a lack of knowledge.

The exemplary communication system 500 shows the 911 database 562located inside the 911 operator center, but it is possible, in alternateembodiments, for the 911 database to be located at a remote location,where several 911 operator centers could share the same database 561.

In accordance with the present invention, the location informationdatabase 561 includes a plurality of landline telephone numbers with anaddress being associated with each of the landline telephone numbers. Italso includes a plurality of telephone numbers used, in accordance withthe present invention, to convey address information associated withedge router ports that may be used by IP telephony devices. In the casewhere a landline phone exists at the location associated with an edgerouter port, an additional entry for the router port need not be enteredin the database 561 with the landline telephone number and addressinformation being sufficient, with calling party number informationsupplied in accordance with the invention, to convey to an emergencyservice operation the address associated with a particular IP call fromthat location. In cases where a landline phone does not exist at thecustomer premise to which a edge router port which may be used for IPtelephony calls is coupled, a dummy telephone number is entered in thedatabase 561 along with the corresponding location of the customerpremises from which IP calls may be placed through the router portassociated with the dummy telephone number. As will be discussed below,by supplying the dummy number as the calling party number for IP callsplaced to the 911 service center, the soft switch of the presentinvention makes it possible for the 911 operator to retrieve locationinformation corresponding to the origin of an IP call even when alandline phone is not present at the location where the IP calloriginated. FIG. 6 illustrates an edge router 600 which may be used asany one of the edge routers 516, 518 of the system illustrated in FIG.5. As illustrated, the edge router 600 includes a CPU 602, packet/frameforwarding engine 606, memory 704 and I/O interface 610 which arecoupled together by a bus 603. The I/O interface 610 includes aplurality of ports used to connect the edge router 600 to variousnetworks. Ports 1 through N are used to couple the router 600 to one ormore Ethernet LANs. Ports N+1 through 2N are used to connect to elementsof the IP network 505, e.g., DHCP server 520 and router R3 522 or R6526, while Ports 2N+1 through 3N are used to coupled the edge router 600to the SMN and thus the LCIS 534 included therein.

The memory 604 includes, an L2 forwarding table 626, an L3 forwardingtable 628, an L2 to L3 address resolution table 624, a frame/packetprocessing and forwarding routine 622, a DHCP session monitoring routine612, address resolution table management routine 614, and port numberinformation routine 618.

The Layer 2 forwarding table 626 includes information used forforwarding received Ethernet frames according to the MAC destinationaddress specified in the frame's header.

FIG. 7 illustrates an exemplary L2 forwarding table 626. The tableincludes a plurality of entries 701, 701′. Each entry includes a MACaddress 702, 702′ and a port number 704, 704′. Under direction of theforwarding routine 622, frames received by the edge router having a MACaddress listed in the L2 forwarding table are output using the port 704,704′ corresponding to the destination MAC address. In this mannerEthernet frames are forwarded in the Layer 2 domain based on MACdestination addresses.

The Layer 3 (L3) forwarding table 628 is used by the router 600 toforward IP packets in the IP domain. As illustrated in FIG. 8, the L3forwarding table includes a plurality of entries 801, 801′. Each entryincludes an IP address 802, 802′, a port number 804, 804′ and aginginformation. The aging information is used to determine when an entry801, 801′ should be deleted from L3 forwarding table as part of a tablemaintenance operation. Under direction of the forwarding routine 622, IPpackets received by the edge router 600 having a MAC address listed inthe L2 forwarding table are output using the port 804, 804′corresponding to the destination IP address. In this manner IP packetsare forwarded in the Layer 3 domain based on IP addresses.

The L2 to L3 address resolution table 624, shown in FIG. 9, is used forconverting between Layer 2, e.g., MAC, addresses and Layer 3, e.g., IP,addresses. The L2 to L3 address resolution table 624 includes aplurality of entries 901, 901′. Each entry includes a MAC address 902,902′, an IP address 904, 904′ and aging information 906, 906′. As in thecase of the L3 forwarding table 628, the aging information 906, 906′ isused for table maintenance purposes.

When an IP packet is received which has a destination address not foundin the L3 forwarding table 628, the forwarding routine 622 compares thereceived IP destination address to the entries in the L2 to L3resolution table 624. If the IP address is listed in the table 624, theMAC address 902 or 902′ corresponding to the received destination IPaddress 904 or 904′, respectively, is retrieved from the L2 to L3address resolution table. The MAC address is then used in a L2forwarding table look-up operation. Using the MAC address as an index tothe L2 forwarding table, an output port to be used for forwarding theinformation included in the received IP packet is determined. As part ofthe forwarding operation, content from the received IP packet is placedinto the payload of an Ethernet frame and then transmitted to theappropriate Ethernet LAN via the port identified in the L2 forwardingtable. In this manner, IP packets received from the IP network can betransmitted to devices over the Ethernet LAN coupled to the edge router600.

In accordance with one feature of the invention, as an alternative tousing address resolution protocol (ARP), the DHCP monitoring routine 611snoops DCHP sessions between devices on the Layer 2 network, e.g.,devices 208, 210 and the DHCP server 220. In this manner, the monitoringroutine 611 obtains information on the assignment of IP addresses todevices and the release of IP address by devices. This information isconveyed to the address resolution table management routine 614 whichupdates the layer 2 to layer 2 (L2 to L3) address resolution table 624.

Address resolution table management routine 614 is responsible forremoving, e.g., deleting, entries from the L2 to L3 address resolutiontable 624 and/or L3 forwarding table, after an entry has aged for apreselected period of time as indicated from the aging informationstored for each entry. Alternatively, in the case where DCHP sessionsare snooped in accordance with one feature of the invention, entries aredeleted tables 624 and 628 when the IP lease time expires, a devicereleases an IP address, or a device fails to respond to a DHCP statusinquiry. Thus, in such an embodiment, IP address entries are added toand deleted from tables 624, 628 based on information obtained fromsnooping communications between host devices on a layer 2 LAN coupled tothe edge router 600 and the DHCP server 220.

Port number information routine 618 responds to port number informationrequests received by the edge router 600 by returning the port numbercorresponding to an IP address or MAC address received in a port numberinformation request.

The routine 618 first determines whether an IP or MAC address has beenreceived in a port number information request. If the request includes aMAC address, the received MAC address is used as an index into the L2forwarding table to determine the router port corresponding to thereceived address. If an IP address is received as part of a port numberinformation request, the IP address is first used as an index as part ofa look-up into the L2 to L3 address resolution table 624. In this mannerthe MAC address corresponding to the received IP address is determinedfrom the table 624. Once the MAC address is determined from table 624 itis used to consult the L2 forwarding table 626. In this manner, therouter port corresponding to the MAC address is determined.

The router port number determined by port number information routine 618is returned to the device which sent the router 600 a port numberinformation request. In the case of a port number information requestfrom the LCIS 534, the determined port number would normally be returnedvia the secure SMN 532 via which the request was received by the edgerouter 600.

FIG. 10 illustrates a DHCP server 520 implemented in accordance with thepresent invention. As illustrated, the DHCP server 520 includes a CPU1002, I/O interface 1004 and memory 1006 which are coupled together bybus 1003. The memory 1006 includes an IP address allocation andmanagement routine 1010, IP to edge router and optionally MAC addresslook-up routine 1012, a pool of available IP addresses 1009, and an IPaddress lease information table 1014. The pool of available IP addresses1009 is a list of unused IP addresses which the DHCP server 520 isauthorized to lease to requesting devices. In accordance with theinvention, the table 1014 is used to manage leased IP addresses and asan IP to edge router (IP2ER) look-up table for providing information onthe edge router associated with an IP addresses.

When a device on a LAN, e.g., device 208 on LAN 204, needs an IP addressso that it can access the IP network 505 it broadcasts an IP addressassignment request. The request is detected by the edge router on theLAN, e.g. router 216. The edge router 516 responds by acting as a proxyof the requesting device 208 and initiating a DHCP session with the DHCPserver 520.

This may be done as is known in the art using DHCP protocol. An IPaddress assignment request conveyed to the DHCP server 520 includes theMAC address of the requesting device. In response to an IP addressassignment request, the DHCP server 520 assigns the requesting device208 an available IP addresses from the pool 1009. In addition the server520 removes the address from the pool 1009 and creates a new entry 1016in the IP address lease information table 1014.

Each entry 1016, 1016′ in the table 1014 includes the IP addressassigned 1020, 1020′, the edge router 1022, 1022′ acting as proxy forthe requesting device, the MAC address 1024, 1024′ of the device towhich the IP address was assigned, and lease time information 1026,1026′. The lease time information 1026, 1026′ indicates the term, e.g.,duration, of the IP address lease and other lease related information.One entry 1016 or 1016′ exists in the table 1014 for each IP addressleased to a device by the DHCP server 520. In the exemplary embodimentof FIG. 10, the table 1014 includes entries for K leased IP addresses1620 through 1620′.

When an IP address is assigned, i.e., leased, to a requesting device,the IP address and lease time information (indicating the duration ofthe lease) is communicated back to the requesting device by way of theedge router acting as the device's proxy.

Accordingly, as part of the DHCP server IP address leasing mechanism, atable 1014 associating assigned IP addresses with informationidentifying the edge router used by the device assigned the IP addressto access the IP network 505 and the devices MAC address.

Edge router information requests, e.g., requests from the LCIS 534, maybe received by the DHCP server 520 via SMN 532. IP to edge routerlook-up routine 1012 is responsible for responding to such requests bycorrelating an edge router to an IP address received in the informationrequest. To determine the edge router corresponding to an informationrequest, the look-up routine 1012 accesses the IP address leaseinformation table 1014 using the received IP address as an index intothe table. In this manner, the look-up routine 1012 retrieves theinformation 1022, 1022′ identifying the edge router corresponding to thereceived IP address. In some embodiments, the routine 1012 also recoversfrom the table 1014, the MAC address corresponding to the received IPaddress. The information identifying the edge router, and, optionally,the MAC address, corresponding to a received IP address is returned tothe device, e.g., LCIS 534, which sent the edge router informationrequest to the DHCP server. In this manner, devices such as the LCIS canobtain from the DHCP server information identifying the edge routerbeing used by a device having a specific IP address.

FIG. 11 illustrates a location and customer information server (LCIS)534 implemented in accordance with the invention. For security reasons,the LCIS 534 is implemented as part of the SMN 532. However, it could,alternatively, be implemented as a device on the IP network 505 assumingsufficient security measures are taken, e.g., the use of a firewalland/or data encryption, to protect the server and its contents fromunauthorized access and/or tampering.

The LCIS 534 includes a central processing unit 1152, I/O interface 1154and memory 1156 which are coupled together by bus 1153. The CPU 1152controls operation of the LCIS under direction of one or more routinesstored in memory 1156. The I/O interface 1154 couples the internalcomponents of the LCIS 534 to external devices via the communicationslinks of the SMN 532. For example, in the FIG. 5 embodiment, the LCIS534 is coupled to the edge routers 516, 518, SS 536 and DHCP server 520via communications links of the SMN 532.

The memory 1156 includes an IP address to DHCP server database 1164, andan edge router and port number to customer information (RPC) database1162, and an information request response routine 1160.

The IP address to DHCP server database 1164, includes informationcorrelating IP addresses which may be assigned by DHCP servers toparticular DCHP servers in the IP network. Thus, the LCIS 534 is able todetermine which DHCP server 520, out of a plurality of such servers, tocontact for information regarding an IP address received as part of aninformation request.

The RPC database 1162 includes information correlating specific edgerouters and ports to customer information including, e.g., physicallocation, name and landline telephone number information.

FIG. 12 illustrates an exemplary RPLC database 1162. As illustrated theexemplary database includes Q records one record corresponding to eachof Q edge routers. Each record includes a router identifier 1252, 1252′and a set of entries corresponding to particular router ports. Eachrouter port entry includes a port identifier 1254, a location identifier1256, customer name information 1258 and telephone number information1260. The location information is the location of the customer premise,e.g., physical LAN location, from which the customer may access the IPnetwork via the identified router and port. The phone number 1260 is thetelephone number of a landline phone located at the correspondingphysical location specified in the edger router/port entry. Additionalcustomer information, e.g. billing, service subscription and level ofdesired privacy information, may also be included in the RPLC database1162 for each router/port entry. The RPLC database 1162 is populated assubscribers contract with an IP service provider for IP service and isupdated, e.g., periodically, to reflect changes in the customerinformation and/or the cancellation or modification of service.

The information request response routine (IRR) 1160 responds to requestsfor location and/or other customer information corresponding to an IPaddress. The IP address of interest and, optionally, the desired type ofinformation, is included in an information request. Such informationrequests may come from a variety of sources, e.g., routers and/orservers implementing security routines, soft switch 536, etc.

An exemplary IRR routine 1160 will now be discussed with reference toFIG. 13. The IRR routine 1160 begins in step 1302 where it is executedby the CPU 1152, e.g., when the LCIS 534 is activated. Then in step 1304the routine 1160 monitors for an information request 1306 including anIP address of interest (IPAOI). For each such detected IP addressinformation request, operation proceeds to step 1307.

In step 1307 the LCIS 534 identifies, e.g., by querying its IP addressto DHCP server database 1164, the DHCP server responsible for leasingthe IPAOI to a device. Then, in step 1308, the LCIS 534 sends a message,including the IPAOI, to the identified DHCP server requestinginformation, e.g., edge router and MAC address information,corresponding to the IPAOI.

In step 1310, in response to the information request sent to the DHCPserver, the LCIS 534 receives edge router identification informationand, in some embodiments, the MAC address of the device to which theIPAOI was leased. Then in step 1312, the LCIS 534 transmits a request tothe edge router identified by the DHCP server for port informationrelating to the IPAOI. The port number information request transmittedto the identified edge router includes, when available, the MAC addressreceived from the DHCP server in addition to, or instead of, the IPAOI.

In response to the port information request message, in step 1314, theLCIS 534 receives from the contacted edge router, the edge router portnumber corresponding to the supplied IPAOI or MAC address. Then, in step1316, the LCIS 534 accesses the RPLC database 1162 using the router andport number corresponding to the IPAOI to retrieve there from therequested location and/or customer information determined to correspondto the IPAOI.

Once the desired information, e.g., customer name, location, telephonenumber is retrieved from the RPLC database, in step 1318 it is returnedto the device which requested information corresponding to the IPAOI.The MAC address may also be returned to the requesting device wheredevice identification information is desired.

Once the requested information corresponding to the IPAOI has beentransmitted to the requesting device, e.g., over the secure SMN 532,processing of the received IP address information request stops in step1320. However, the monitoring operation of step 1304 and processing ofother IP address requests will continue until the routine 1160 isterminated, e.g., by the LCIS 534 being turned off or shut down.

The soft switch 536 of the present invention supports many applicationsand allows calls to be routed between the IP and PSTN domains. Whenrouting calls to emergency service centers as identified by, e.g., thecalled telephone number, e.g., 911, it is desirable that the soft switch536 convey information to the service center that allows the emergencyservice center to determine the physical location from which an IP callwas placed, e.g., so that emergency service personal can be dispatchedto the location. As will be discussed below, the soft switch 536achieves this by including a telephone number corresponding to thelocation from which an IP call was placed in the calling partyinformation field of calls routed by the soft switch to an emergencycall center. In cases of calls routed to other numbers in the PSTNdomain, the soft switch inserts the telephone number of the IP telephonydevice from which a call was placed in the calling party informationfield of an SS7 call generated from the IP telephony call.

FIG. 14 illustrates an soft switch 536 implemented in accordance withthe present invention which supports the emergency call feature of thepresent invention which allows a emergency call service center todetermine the location of the IP caller from calling party telephonenumber information associated with a call.

As illustrated in FIG. 14, soft switch 536 includes CPU 1458, routingengine 1454, switching circuitry 1456, PSTN gateway 1460, and memory1452, which are coupled together by bus 1490. In the FIG. 14 embodiment,the PSTN gateway 1460 is illustrated as part of the soft switch 536.However, it may be, and often is, implemented as a separate entity whichis coupled to the soft switch 536. Accordingly, the FIG. 14 embodimentis intended to be exemplary but in no way limits or requires, forpurposes of the invention, that the PSTN gateway 1460 be implemented asan element of the soft switch 536.

CPU 1458 controls soft switch operation under the direction of one ormore routines stored in memory 1452. The various routines will bediscussed further below. Routing engine 1454, using switching circuitry1456 receives and transmits data from the IP base network 505, e.g.,under control of CPU 1458. This data includes, for example voice datacorresponding to IP telephone calls. The routing engine 1454 is coupledto the SMN 532 through the switching circuitry 1456 and can receive andsend information and other signals over the SMN 532. The SMN 532includes the LCIS database 534, which the soft switch 536 uses to obtaina telephone number corresponding to a location from which a call to anemergency service center was placed in accordance with one feature ofthe present invention. Address information corresponding to the physicallocation from which an IP telephony call was placed, e.g., to anemergency call service center may also be obtained from the LCISdatabase 534.

The soft switch's PSTN gateway 1460 serves as an interface between theIP domain and the SS7 domain which comprises the PSTN. The PSTN gateway1460 converts the IP packets of an IP call directed to a destination inthe PSTN to an SS7 signal format for transmission over the PSTN. Thisincludes placing calling party information, e.g., a calling partytelephone number, into one of the control fields associated with a SS7call. Voice data is converted into voice signals which are transmittedin accordance with the SS7 standard as the voice portion of a call. Thegateway 1460 also converts SS7 signals into IP packets for transmissionto an IP telephony device. Thus, the gateway 1460 is responsible forconverting between IP packet and SS7 signal formats for purposes ofcompleting a call extends between the IP network and the PSTN. Whileshown as an element of the soft switch 536, the PSTN gateway 1460 can beimplemented as a separate module from the soft switch. In one suchembodiment multiple soft switches are coupled to the PSTN gateway. Inthis configuration, a plurality of soft switches can share the same PSTNgateway for purposes of transmitting calls to, and receiving calls fromthe PSTN 531.

The soft switch's memory 1452 includes operating system 1466, IPaddress/telephone number registration/management routine 1472, activedevice information 1462, call processing routine 1468, IPaddress/telephone number information 1470, and soft switch E911 routine1472.

As discussed earlier, each device coupled to the Ethernet, e.g. device 1208, obtains an IP address, when it needs to communicate over IP network505 if it does not already have one assigned to it. If device 1 208 isan IP telephone, in addition to obtaining an IP address it alsoregisters with the soft switch 536. IP address/telephone numberregistration/management routine 1471 is responsible for registeringactive IP telephony devices and storing the current IP address to beused when routing calls to/from the telephony device. It is alsoresponsible for performing billing operations and for deleting entriesfrom the active device information table 1462 when they log out or theIP address aging information indicates the stored IP addresscorresponding to a particular telephone number is no longer valid. Aspart of the registration process, the registering telephony device isauthenticated to make sure it authorized to send/receiver callscorresponding to the telephone number the device provides.

After authentication, the registration/management routine 1471 storesthe telephone number 1474 corresponding to a registering device alongwith the IP address 1476 assigned to the device and the corresponding IPaddress aging information 1480 in the active device information table1462 maintained in memory. In FIG. 14, the table 1462 includesinformation corresponding to a D active devices with the informationcorresponding to each active telephony device being stored in adifferent row of the table 1462.

Using the active device information stored in table 1462 as a result ofthe registration process, the soft switch is able to route callsdirected to the telephone number of an active IP telephony device byretrieving the corresponding IP address from table 1462 and routing thecall over the IP network based on the retrieved IP address. Thus, theregistration process and the resulting information stored in table 1462allows device 1 208 to communicate with other telephones, and allows theIP service provider to keep track of the IP telephony users for billingand/or other purposes.

Call processing routine 1468 is used to process calls which are routedby the soft switch 536. Call processing routine 1468 uses IP/telephonenumber information 1470, active device information 1462 and, in the caseof a call to an emergency call service center SS E911 routine 1472 toprocess a call. IP address/telephone number information 1470 includesinformation used to distinguish between telephone numbers correspondingto IP telephony devices and telephone numbers corresponding to the PSTN531.

In one exemplary embodiment, when a user enters a telephone number on anIP phone, e.g., to place a call, the IP phone is connected to a localsoft switch 536 for call routing purposes. Once a calling party iscoupled to the soft switch 536, call processing routine 1468 becomesresponsible for handling call routing.

Soft switch 536 uses IP address/telephone number information 1470 todetermine if a dialed number is an IP telephone number or a PSTNtelephone number. If the number is an IP number the call is routed usingthe routing engine 1454 and IP address information obtained from activedevice information table 1462 or a similar table maintained, e.g., byanother soft switch 536. If the dialed number is to a PSTN telephonenumber the call is routed through the PSTN gateway 1460 with a telephoneswitch in the PSTN determining ultimate call routing for the PSTNportion of the call. Calls routed through the PSTN gateway from the PSTNare routed in the PSTN domain under direction of call processing routine1468 in the same manner calls are routed from one IP telephony device toanother. Thus, incoming telephone calls from both the IP-based telephonenetwork and the PSTN are sorted, checked and subject to protocol/formatconversion, if necessary, by the call processing routine 1468.

As part of normal call routing procedure, the call processing routine1468 checks to determine if a call from an IP telephony device isdirected to a telephone number corresponding to an emergency callcenter, e.g., a 911 call center, connected to the PSTN. When such callsare detected, e.g., based on the entered telephone number, e.g., 911,the call processing routine calls soft switch E911 routine 1472.

Thus, soft switch E911 routine 1472 is activated in response to the softswitch receiving a call to a telephone number it knows, e.g., based onstored information, corresponds to an emergency service center. A 911call from an IP telephony device is an example of a call that triggersprocessing by the E911 routine 1472. This routine 1472 allows mobile IPtelephone users to make emergency, e.g., 911, which will be suppliedwith a calling party ID, e.g., telephone number, corresponding to thelocation from which the call is placed before the call is routed to theemergency call service center via the PSTN 531. This allows an operatorat the emergency call service center to obtain calling party locationinformation based on the calling party number through a simple databaselook-up operation as done for normal landline calls. Thus, in accordancewith the present invention calls to emergency call centers in the PSTNdomain have the calling party number set to match the physical locationfrom which the call was placed as opposed to the telephone number of theIP telephony device used to place the call. Soft switch E911 routine1472 will be discussed in detail in regard to FIG. 16.

FIG. 15 illustrates an exemplary 911 emergency call service center,e.g., a 911 operator center 560. The service center 560 can be used inaccordance with the present invention to provide emergency telephoneservice to IP and/or PSTN telephone users coupled to the center 560 viathe PSTN 531. The center 560 includes a plurality of operatorworkstations 1 through N 1502, 1504, and a location informationdatabase, e.g., a 911 database 562. The 911 database 562 includes phonenumbers 1506, 1506′, and corresponding locations, e.g., addresses ofservice subscribes. In accordance with the present invention some phonenumbers correspond to landline phones. In other cases the phone numberscorrespond to numbers used to convey address information about customerpremises from which an IP telephony device may operate. Such telephonenumbers may be described as dummy or non-routing telephone numbers sincethey are not used for call routing purposes but to allow a 911 operatorto retrieve location information corresponding to an IP servicesubscriber location in the event an emergency call is placed from theservice subscriber's location, e.g., customer premises. Unique numbers,e.g., with a particular set of starting digits, may be used todistinguish non-routing numbers from landline telephone numbers therebyenabling an emergency service center operator to distinguish between atelephone number which can be used to contact a party and a telephonenumber which can be relied on for address retrieval purposes but nottelephone contact purposes. In accordance with the invention, IPcustomer premise location information and an associated non-routingtelephone number is added to the 911 database when the IP servicesubscriber 535 signs up for IP service assuming the database does notalready include the telephone number of a landline phone located at thesubscriber premises.

The telephone number of the IP telephony device may, and in oneembodiment is, inserted by the soft switch into an SS7 signal field usedto indicate a telephone from which a call is forwarded for IP telephonycalls directed to an emergency call service center. In such anembodiment the service center is provided with the telephone number ofthe IP telephony device used to place the call in addition to thenon-routing telephone number to be used for location determinationpurposes. Since, in some embodiments, the service center can determinefrom the format or value of the non-routing telephone number that it isa number which is not to be used for contact purposes, in such cases theoperator can default to using the telephone number included in the callforwarding indicator field of the SS7 call to determine a telephonenumber which can be used to contact the calling party.

While shown as part of the service center 560, it is to be understoodthat the 911 database 562 may be located external to the center 560 andmay be shared by multiple emergency call centers.

Working at an operator workstation 1502, an emergency call operator usescalling party telephone number information, also known as automaticnumber identification information, included in a received call to accessthe 911 database 562. Using the calling party telephone number, theoperator retrieves the corresponding physical location information,e.g., address, which identifies the customer premises 531 from which anemergency call was placed to the center 560. The operator then uses, inmany cases, the retrieved address information to dispatch an emergencyaid worker, e.g., police and/or ambulance, to the identified location.

The steps of an exemplary soft switch E911 routine 1472 implemented inaccordance with the present invention will now be discussed withreference to the flow chart of FIG. 16. The soft switch E911 routine1472 begins in step 1602 where it is executed by the CPU 1458, e.g.,when a call to an emergency service center, e.g., a 911 call, isdetected by call processing routine 1468. Next, in step 1608, the softswitch 536 queries a location and customer information server (LCIS) 534for telephone number and/or address information correlating to thecalling party's IP address and/or calling telephone number. The IPaddress and/or telephone number of the calling party, included in thequery is used by the LCIS 534 to determine the physical location, e.g.,customer premises, from which the call was placed. This information maybe retrieved by the LCIS 534 using the techniques described above.

In step 1610, the soft switch 536 receives from the LCIS 534 thecustomer information, e.g., telephone number, corresponding to thecustomer premises from which the IP telephony call was placed. Thereceived telephone number may be a landline telephone number or, in thecase where a landline telephone in not present at the customer premises,a non-routing telephone number used for conveying location information.

In step 1612, the telephone number included in the received informationis loaded into the calling party field of the 911 call. This makes thecall appear as if it is originating from the physical location of the IPdevice. In step 1612, in some embodiments, the telephone number of theIP telephony device may be copied into a field normally used to convey atelephone number corresponding to a line through which a call wasforwarded.

In step 1614, the soft switch 536 transmits the 911 call to the 911operator center 560 located in the PSTN. The routine stops in step 1616.

When the 911 call is received at the 911 operator center 560, the callis routed to one of the operator workstations 1502, 1504. The 911operator workstation will then use normal 911 routines to determine thephysical location of the telephone number in the calling party of the911 call. Since the IP telephone number was transmitted with thetelephone number corresponding to the physical location of the IPtelephone in the calling party field of the call, the operatorworkstation 1502 can locate the physical location of the IP telephoneallowing emergency help to be dispatched to the correct location.

It is to be understood that numerous variations on the above describedmethods and apparatus are possible without departing from the scope ofthe invention.

What is claimed is:
 1. A method of servicing an IP call from an IPtelephony device, the method comprising the steps of: determining atelephone number associated with the physical location from which the IPcall originated, wherein said determined telephone number is a telephonenumber that is not used for call routing purposes but is stored in alocation information database in association with an addresscorresponding to the determined physical location; transmitting saidcall to a telephone call service center with call originationinformation including said determined telephone number, said callservice center being an emergency call service center; and using thedetermined telephone number to retrieve, from a database includingtelephone numbers and associated location information, addressinformation corresponding to the physical location from which the callwas placed.
 2. The method of claim 1, wherein transmitting said call toa telephone call service center includes: converting said call from anIP packet format to an SS7 format; and including in SS7 signalinginformation associated with the voice portion of the call, calling partyidentification information including said determined telephone number.3. The method of claim 1, further comprising: dispatching a rescueworker to an address included in the retrieved address information.
 4. Acommunications system comprising: an edge router including ports coupledto IP telephony devices; a soft switch coupled to said edge router, thesoft switch being for routing calls from said IP telephony devices; acall service center for servicing telephone calls; a locationinformation database coupled to said call service center, the locationinformation database including: telephone numbers corresponding tolandline telephones, a physical location being associated in saiddatabase with each landline telephone number; and non-routing telephonenumbers corresponding to locations of IP service subscribers, addressinformation corresponding to a physical location being associated insaid database with each non-routing telephone number; and wherein saidsoft switch includes: means for determining a telephone numberassociated with the physical location from which an IP call originated;and means for transmitting IP calls to said call service center withcall origination information including said determined telephone number.5. The system of claim 4, wherein said non-routing telephone numbers arenot used in said systems for call routing purposes.
 6. The system ofclaim 4, further comprising: a PSTN telephone switch coupled to saidsoft switch for processing telephone calls having an SS7 call format,calls in said SS7 format including voice and control signals.
 7. Thesystem of claim 6, wherein each of said non-routing telephone numbershas a format which is different from the format of said landlinetelephone numbers.
 8. The system of claim 4, further including said IPtelephony devices, at least some of said IP telephony devices beinglocated at different physical locations.
 9. A method of servicing an IPcommunication from an IP device, the method comprising the steps of:determining a non-routing telephone number associated with the physicallocation from which the IP communication originated, wherein saiddetermined non-routing telephone number is a telephone number that isnot used for call routing purposes but is stored in a locationinformation database in association with an address corresponding to thedetermined physical location; transmitting said determined non-routingtelephone number as part of a telephone call to a telephone call servicecenter with said determined non-routing telephone number being providedto said service center as a call origination telephone number, said callservice center being an emergency call service center; and using thedetermined non-routing telephone number to retrieve, from a databaseincluding telephone numbers and associated location information, addressinformation corresponding to the physical location from which the IPcommunication originated.
 10. The method of claim 9, whereintransmitting said determined non-routing telephone number to a telephonecall service center includes: converting said IP communication from anIP format to an SS7 format; and including in SS7 signaling informationcalling party identification information including said determinednon-routing telephone number.
 11. The method of claim 9, wherein saidemergency call service center is a call service center which services911 telephone calls.
 12. A system for servicing an IP call from an IPtelephony device, the system comprising: a switching device configuredto: determine a telephone number associated with the physical locationfrom which the IP call originated, wherein said determined telephonenumber is a telephone number that is not used for call routing purposesbut is stored in a location information database in association with anaddress corresponding to the determined physical location; and transmitsaid call to a telephone call service center with call originationinformation including said determined telephone number, said callservice center being an emergency call service center; and said callservice center, said call service center being configured to use thedetermined telephone number to retrieve, from a database includingtelephone numbers and associated location information, addressinformation corresponding to the physical location from which the callwas placed.
 13. The system of claim 12, wherein said switching deviceimplements a soft switching operation.